The present invention relates to cache memory management and snapshot operations in a data storage system.
This application incorporates herein by reference U.S. application Ser. No. 10/354,797 entitled, Methods and Systems of Host Caching, filed on Jan. 29, 2003.
A data storage system may use snapshots for backup, data mining, or testing of software programs in development. A snapshot is a usable image of the data at an instant in time. The snapshot results in two data images: (1) the original data that can be read and written by applications as soon as the snapshot is created, and (2) the snapshot that can be backed up or mined. Some techniques allow a snapshot to be modified while others create read-only images. One technique of snapshot is copy-on-write. In copy-on-write, upon getting a request to store modified data, the data storage system first copies the original data to a target storage space before permitting the modification to be written to its source storage space. The need for high data availability in data storage systems may require making frequent snapshots of data. However, frequent snapshots consume system resources such as cache memory, the internal memory bandwidth, storage device capacity and the storage device bandwidth.